1. Field of the Invention
The invention relates to a method for establishment of working characteristics relevant to the operation of an internal combustion engine, especially an internal combustion engine installed in a vehicle, and in particular, the signal pattern based on the crank angle representing the combustion chamber pressure. The invention also related to a device to execute this method.
2. The Prior Art
Such methods and devices, as well as the execution of these methods, are known in the art and they communicate currently with an angle reference-wheel arranged most often on a crankshaft or a camshaft rotatably joined thereto, whereby the angle reference positions arranged in a specific angular pitch are scanned by a respective sensor and processed correspondingly in an evaluation unit. There are special angle-reference triggers used in the area of engine research and development, which make possible a very accurate triggering of the used index measuring system up to the range of 0.1xc2x0 to 0.5xc2x0 crank angle (KW), but which is complicated and costly and not usable in vehicles (for on-board engine control). On the other hand, there are currently used the so-called crankshaft trigger wheels with the common 6xc2x0 circular pitch in teeth for various applications of internal combustion engines, which are installed as drive engines in vehicles, whereby two teeth are missing to make possible an absolute angle assignment (60xe2x88x922=trigger wheel). Signal detection with high crank-angle discrimination in real-time and with little time delay is thereby not possible, and for this reason, the precise methods and devices widely and commonly used in the index measuring technology cannot be employed.
It is the object of the present invention to avoid the aforementioned disadvantages of methods and devices known in the art and to provide particularly a possibility to make use of the precise methods and devices known from the index measuring system with simple, cost-effective crank-angle trigger wheels that are suitable for vehicles as well.
This object is achieved according to the present invention with a method of the aforementioned type in that the working characteristic is measured time-based with high time discrimination and which is transformed to a crank angle basis with the aid of a time and angle-based crank-angle signal of low angle discrimination under interpolation, and whereby there is assigned to the top dead center (OT) of the respective cylinder, by a multiple, a freely selectable angle increment under interpolation with high angle discrimination. The time-equidistant received sensor signal of the monitored working characteristic can thus be transformed, in a simple way, into an angle-equidistant signal whereby the actually resulting xe2x80x9ctransformation ratioxe2x80x9d is arbitrary to a large extent.
According to an especially preferred embodiment of the inventive method, the transformation is performed based on the crank angle under consideration of rpm- and/or angle-dependent correction values, which are preferably obtained under defined load conditions without the rpm-fluctuations caused by the [vehicle] operation, e.g., in an engine trailing throttle state, especially under the use of the symmetric pressure pattern during engine trailing throttle state at open throttle, whereby the angle of the maximum cylinder pressure (detected by intersection method) to the top center (OT) of the engine has a rpm-dependent offset value, which is used for correction. Time values can be determined from the time information of the signal flanks of the crankshaft trigger-wheel sensor (signal flanks cause an interrupt routine in which the actual timer value is placed in intermediate storage) and of the time information of the working characteristics signal (scanned before, between and after said flanks), and under consideration of correction values, e.g., rpm- and angle dependent correction characteristic, whereby said time characteristics are strictly assigned to the top dead center of the respective cylinder (and not the signal flanks of the trigger wheel) by a multiplexe2x80x94e.g. 0.5xc2x0 crank anglexe2x80x94of a freely selectable angle increment. Precision can be achieved, particularly in reference to angle-offset errors, with the use of correction values, which are given automatically in defined load conditions, as in the above-mentioned engine trailing throttle state, and which offer results comparable to the above-mentioned precise bench test indexing.
In an especially preferred embodiment of the invention, a cylinder pressure curve in the range up to the start of combustion of the respective cylinder, determined by thermodynamic calculation methods, is compared to an actual cylinder pressure curve, which is determined in turn by means of a pressure sensor, whereby the respective absolute crankshaft angle is computed with a discrimination in the range of an approximately 1xc2x0 crank angle (KW). Thus, it is possible, for example, to use a (toothed) trigger wheel on the crankshaft without synchronization elements (the above-mentioned missing two teeth for determination of the absolute angle position), which makes manufacturing of the trigger wheel easier, on one hand, and which increases, on the other hand, the angle information at the position of the otherwise provided gap (6xc2x0 instead of 18xc2x0 flank width). Additionally, this embodiment makes directly possible the use of the flywheel ring gear of the internal combustion engine as a trigger wheel in many applications.
At this point it must be mentioned that the invention is not limited, of course, to the above-mentioned example having the combustion chamber pressure as a relevant working characteristic. The determination of the highly discriminated position of a reference signal relative to the crankshaft angle, made possible by the invention, is additionally of great advantage practically at all synchronous crankshaft-influenced values, which are determined by sensors at the corresponding positions in the motor areas, such as the suction pressure, the exhaust pressure, the air mass flow, the measured values from vibration sensors and knocking sensors, and the like.
According to an especially preferred additional embodiment of the invention, the interpolation is performed in a linear manner through implemented functions, whereby the time for calculations is saved and a very small shift in time can be achieved. The resulting shift in time is thereby determined essentially only by the number of teeth on the trigger wheel or by the time span between consecutive trigger signals.
The time-based pick-up of the working characteristic occurs in further embodiments of the invention with a discrimination dependent on the dynamics, preferably in the range of approximately 10 to 50 microseconds. Crank-angle-based discrimination can be achieved therebyxe2x80x94as already mentioned abovexe2x80x94which allows the use of methods and devices known from the indexing technology.
Mounting errors of the trigger wheel and sensor can be continuously corrected during operation on a crank angle basis during transformation and interpolation of the time-based, recorded working characteristic. By mounting error there is to be understood the angle shift between one parameter value strictly predetermined for all vehicles of one series (e.g., the position of the first tooth of the trigger wheel after the gap relative to the top dead center of a cylinder of the engine) and the true angle-offset value based on the tolerance during manufacturing and installation of the trigger wheel together with the transfer behavior of the respective position sensors (transformation of the changing magnetic field based on the trigger wheel into the sensor output signal and zero-passage signal detection).
An inventive device for carrying out the described method is provided with a timely and highly discriminating sensor for the relevant working characteristic, a crank angle sensor of low discrimination (standard crank angle sensor), which is preferably a trigger wheel on the crankshaft having 60 minus 2 teeth together with the respective pick-up sensor, and a transformation- and interpolation element being in communication with the working characteristic sensor and the crank angle sensor, whereby said transformationxe2x80x94and interpolation element establishes the highly discriminating signal pattern of the working characteristic. This makes possible a simple and compact arrangement, which may be easily mounted in a vehicle for which the internal combustion engine is installed as drive.
According to the preferred embodiment of the invention, the transformation- and/or interpolation element may be integrated either in the motor control of the internal combustion engine or in a micro-electric unit that is preferably housed in one of the measuring amplifiers, in one of the connectors, or in one of the sensors itself, which further simplifies the arrangement in a vehicle.
The invention will now be described in more detail with the aid of accompanying drawings.